Diverter valves through which corrosive fluent materials are conducted have been traditionally constructed with components made of cast bronze or other expensive corrosion resistant metal alloys, and also incorporate components made of fiber-reinforced thermoplastics such as Teflon to provide sealing surfaces. Such valves have nevertheless exhibited numerous operational problems such as poor fire performance due to melting of valve seats, as well as scaling and galvanic corrosion, and melting of protective coatings due to thermal conductivity of a metallic valve housing. It is therefore an important object of the present invention to provide a diverter valve assembly of the foregoing type which is capable of more effectively handling corrosive fluids and solid waste slurries while safely reacting to conduit shock loads typically experienced in marine vessel installations.